The present invention relates in general to automatic cap-fitting apparatus.
More particularly, the invention relates to a device for checking the fitting of a threaded cap onto a container, the device being associated with automatic cap-fitting apparatus, particularly of the carousel type, including rotatable support means which can move at least one container about a principal axis of the apparatus and at least one screwing head for screwing a cap onto a respective container so as to close the container as a result of its movement about the principal axis, in which each screwing head is arranged to screw a cap onto a container with a predetermined tightening torque.
Automatic cap-fitting apparatus consists of machines which can tighten caps or stoppers onto the mouths of packaging containers, for example, of the type for containing consumable substances such as drinks. Some known types of cap-fitting apparatus for fitting threaded caps perform the operation to fit each cap onto a respective container whilst the container is travelling along a circular path, and these types are therefore generally known as carousel-type cap-fitting apparatus.
A known carousel-type cap-fitting apparatus is shown in appended FIGS. 1 to 3 which are a general front elevational view of the apparatus, a plan view of the apparatus viewed from the line II—II of FIG. 1, and a sectioned side elevational view of a screwing head of the apparatus, respectively.
The cap-fitting apparatus of FIG. 1, which is generally indicated 1, comprises a base 2 on top of which there is a unit 3, including a rotatable platform 3a, for supporting a plurality of containers 5, for example, bottles. The containers 5 are supplied to the platform 3a by means of a conveyor belt 7 of a packaging line (which is not shown since it is of generally known type).
The apparatus 1 further comprises a central pillar 8 which has a principal axis X and is rotated by a drive unit M housed in the base 2. A plurality of screwing heads 9 (only two of which are visible in FIG. 1) are associated with the pillar 8 so as to be movable in the same direction as the platform 3a along a circular path concentric with the axis X.
In particular, the heads 9 are movable relative to an upper framework 10 of the apparatus 1 which is connected to the base 2 so as also to be stationary. Associated with the framework 10 is a device 11 for supplying caps 11a withdrawn from a store (not shown) to the position in which each cap is to be coupled with a respective container 5 by being screwed thereon.
During the supply of a container 5 to the apparatus 1, the container is initially disposed on the conveyor belt 7 by which it is brought to the vicinity of a feed screw 13 in order to be engaged by a recess of a star-shaped toothed wheel 15. The wheel 15 is rotated by a respective shaft 15a which is also driven by the drive unit M. The container 5 is then brought to a position in which is engaged by a recess of another star-shaped toothed wheel 17 fixed for rotation with the central pillar 8 and thus rotatable about the axis X, the container 5 being supported on the rotatable platform 3a in a manner such that, whilst it follows an arcuate path about the axis X, a screwing head 9 can tighten a cap 11a onto the container. U-shaped support brackets 8a fixed to the pillar 8 may also be provided for engaging a region close to the mouth of each container 5 and thus holding it firmly in the erect position during the screwing operation. Upon completion of the operation to screw on the cap 11a, the container 5 is engaged by another star-shaped toothed wheel 19, the rotation of which is controlled by a shaft 19a driven by the drive unit M, in order to be returned to the conveyor belt 7, on which the container will continue towards a subsequent station of the line.
With particular reference to FIG. 3 of the drawings, each screwing head 9 comprises an upper portion 25 and a lower portion 27. The upper portion 25 has a roller 21 mounted for rotating about a radial axis, relative to the axis X, and slidably engaging a cam track 23 which has a descending portion and an ascending portion, with reference to the axis X, and has a pair of opposed working surfaces. A bush 25a fixed for rotation with the lower portion 27 of the head 9 is suspended on the portion 25 for rotation about an axis perpendicular to that of the roller 21, by means of a rolling-contact bearing. The portion 27 is substantially sleeve-shaped and has, on an outer surface, a set of axial teeth 29 for engagement by a corresponding set of teeth of a gear 31. The gear 31 in turn is connected rigidly to another gear 33, the teeth of which mesh with the corresponding teeth of a ring gear 35 having internal teeth and supported by stationary pillars 10a of the upper framework 10 of the apparatus 1.
As a result of the rotation of the central pillar 8 of the apparatus 1, each screwing head 9 thus performs, in addition to its revolving movement about the axis X, a rotary movement about its own axis with a multiplication factor, relative to the rotation of the pillar 8, determined by the transmission ratio between the ring gear 35 and the gear 33, and between the gear 31 and the set of teeth 29.
A cup-shaped element 37 bearing a ring 37a, for example such as an O-ring, for gripping a cap 11a to be screwed on is connected to the lower portion 27 of the screwing head 9. The element 37 is normally connected for rotation with the portion 27 but, by virtue of the presence of a release device of known type, generally indicated 39, can be released therefrom when a predetermined value of the torque with which a cap 11a is tightened onto the respective container 5 is reached. In particular, the device 39 may comprise two mutually facing disk-shaped elements 41 which perform the function of a mechanical, magnetic, or electromagnetic clutch, in known manner. Alternatively, each head 9 may itself comprise a dedicated electric motor (not shown in the drawings) so that the speed of rotation of the head can be varied by control of the intensity of the current supplied to the motor and, in this case, the current can be regulated in a manner such that it becomes zero at a predetermined value of the torque with which a cap 11a is tightened onto the respective container 5.
A thrust rod 43, arranged coaxially along each head 9 with the ability to slide axially, is mounted by means of a respective revolving-contact bearing so as to be rotatable relative to a supporting portion 43a slidable relative to the upper portion 25 of the head 9. The supporting portion 43a has a roller 45 which is rotatable about a radial axis, with reference to the axis X, so as to engage for sliding on a cam surface 47 integral with the cam track 23. Moreover, a helical spring 49 interposed between the cup-shaped element 37 and an abutment ring fixed to the rod 43 urges the rod towards the cam surface 47 so as to keep the roller 45 in engagement with this surface.
When a cap 11a has been screwed onto the respective container 5 by the head 9, the shape of the cam 23 causes the screwing head 9 to be raised by means of the roller 21 whilst the surface of the cam 47 brings about a downward movement of the thrust rod 43, by means of the roller 45, so that, during the downward movement of the thrust rod 43, its end remote from the portion 43a releases the lower cavity of the element 37 from any cap 11a remaining associated therewith.
In FIG. 2, the operative steps of a head 9 of the apparatus 1 are indicated schematically, purely by way of example, with particular reference to the case of a cap 11a having a thread with a single start.
Starting from the position bearing the reference 0, the head 9, which moves clockwise with reference to the drawing, moves to the position S (start) covering an arc A the extent of which is normally about 70°. Whilst the screwing head 9 is moving along the path A, a container 5 is supplied to the apparatus 1 by means of the belt 7, the screw 13, and the star-shaped wheel 15, and a respective cap 11a is supplied, by means of the device 11, to the position above the container 5 on which it can be engaged by a screwing head 9.
Between the positions S and ON, the screwing head 9, with the respective cap 11a, is moved downwards as a result of the engagement of the roller 21 with a descending portion of the cam 23 until the cap 11a is positioned adjacent the threaded neck of the container 5. This stage, which is performed along the portion of the arcuate path indicated B, normally has an angular extent of about 30°.
An arc C having an angular extent of about 100°, along which the cap 11a is normally screwed onto the container 5 to the predetermined tightening torque, extends between the positions ON and OFF.
In the subsequent portion of the arcuate path D which extends between the positions OFF and R (result) through an angle of about 60°, the head 9 is raised and released from the cap 11a and from the container 5. If the head 9 is of the electromagnetic type, its electrical disconnection takes place, and the supply to its motor is thus stopped, along the path D.
In the arcuate portion E which extends between the positions R and 0 and the angular amplitude of which is normally about 100°, the container 5a which has just been capped is discharged from the apparatus 1 and returned once more to the conveyor belt 7 by means of the star-shaped wheel 19.
Known apparatus of the type described above cannot normally check that the operation to screw a cap onto the respective container has been performed correctly without this leading to considerable complexity of the apparatus. In particular, in the most common case, it is necessary to provide an additional checking station downstream of the apparatus 1 in order for this operation to be performed by suitable personnel so that containers which have been closed incorrectly can be removed.
It is in fact inevitable that, as a result of the automatic screwing of the threaded caps onto the respective containers, some of the caps will be fitted incorrectly, and there is therefore a reject rate which, although it is small, is not zero. The average reject rate for apparatus which has been operating for a few years and which has undergone good and regular maintenance, may be of the order of 4-8%. The causes of rejection are normally the following:                a missing cap and/or container, which has disappeared for accidental reasons after passing presence sensors disposed upstream of or adjacent the machine;        crooked supply of a cap, that is, with its axis not coaxial with that of the thread on the mouth of the container;        an incomplete or faulty thread and/or closure surface of the container or of the cap;        a cap and/or a threaded container mouth with longitudinal splits;        rotation of a container as a result of the rotation of the respective screwing head;        faulty restraint of the cap by the screwing head so that relative slippage takes place between the cap and the head.        
As a result of an analysis of the causes of rejection indicated above, it has been concluded that each of these causes leads to a well-defined outcome of the operation to screw on the cap. In particular, if the container or the cap is missing, if the container is rotated by the screwing head, or if the cap is not fixed correctly relative to the head, the screwing head does not succeed in reaching the predetermined tightening torque within the arcuate interval C; when a cap is supplied crooked, the predetermined tightening torque is reached in a region preceding the start of the arcuate interval C, that is, before the ON position; if the threads or the contact surfaces between the cap and the container are uneven or if the mouth of a container or a cap are split, the predetermined tightening torque is reached after the OFF position.
It has therefore been concluded that the operation to screw on the cap can be considered to have been performed correctly and the respective container 5a can be considered “good” only when the predetermined torque for the tightening of a cap onto the respective container is reached within the angular interval C, that is, between the positions ON and OFF, whereas in all other cases, the container 5a should be considered “not good” and therefore rejected downstream of the apparatus 1.